For a number of years there has been a demand for coloured or tinted contact lenses, whether this is for identification purposes, protection of the user against bright light, or for cosmetic purposes, (not only to enhance the natural colouring of the eyes, but sometimes to conceal disfigurements).
The production of contact lenses to fulfill all the various demands, and which have a natural appearance to a viewer is demanding from a technical viewpoint and has been testing the industry for a number of years. The problems involved include the fact that colourants must be incorporated into the lens without affecting the optical properties of the final product, the colourants must resist leaching out in storage and cleaning, (including auto-claving) and must not undergo decomposition or react chemically with, or in, the presence of reagents used in daily cleaning and disinfection of the contact lens. Further they must also resist fading upon prolonged exposure to light, such as intense sunlight, and must be non-toxic and physiologically inert, as well as mechanically non-irritating.
From a commercial standpoint, it is necessary that the colouring or tinting of the contact lenses can be carried out in a cost effective manner, therefore the process used should not be so complex, time consuming or labour intensive as to be impractical.
One particular problem encountered with the production of such tinted lenses arises from the fact that the natural appearance of the human iris is not a simple solid colour, but consists of a patterned structure involving many shapes and colours which in order to provide a contact lens of natural appearance should be mimicked. Therefore, coloured lenses having a solid colour in the iris area have the disadvantage of producing an unnatural appearance when fitted in the eye.
U.S. Pat. Nos. 4,582,402 and 4,704,017 (Both Knapp) disclose coloured lens having a dot matrix pattern applied to the iris area, using offset pad printing techniques. However, in the process disclosed in these patents, the lens must first be produced, and then, in an added manufacturing segment, the pigment pattern is prepared and transferred to the surface of the previously prepared lens. Following this, the lens is subjected to further treatment to fix the pigment to the surface of the lens and render it resistant to leaching, abrasion, fading, and the like.
U.S. Pat. No. 4,668,240 discloses a process in which a colouring substance and a binding agent are printed on the surface of a contact lens in an iris simulating pattern. Here again, however, the lens must be first produced, and the printing accomplished in a series of additional steps to the manufacture.
In co-pending application Ser. No. 469,007, filed Jan. 29, 1990, now abandoned, an improved procedure is described in which the colourant is applied to the optical surface or surfaces of the casting mould in which the contact lens is to be formed. This procedure involves the use of a colouring material that is insoluble in the monomer material from which the lens is to be manufactured, dispersing the colouring material in a carrier system which is compatible with the monomer material (and may comprise the monomer from which the lens blank is to be made), and applying the dispersed colourant/carrier material on one or more surfaces of the casting mould. The basic monomeric material from which the lens is formed is introduced into the mould and contacts the surface, or surfaces, and the material is then polymerized to produce a lens blank having the coloured material impregnated in the blank, adjacent to one or both optical surfaces thereof. The procedure not only enhances the preciseness and reproducibility of the end product, but it also permits the colouring step to be incorporated as an integral part of the manufacturing process, rather than having to perform a subsequent and separate manufacturing operation.
However, in instances where the casting mould is made of a hydrophobic material, such as polyolefin, it has been difficult to apply the pigment dispersion to the mould surfaces, particularly in circumstances where the pigment carrier is a hydrophilic monomer material. Consequently, there is a need for a method of modifying the character of the hydrophobic surface of the casting mould in order to improve the acceptability of the hydrophilic pigment carrier applied to the surfaces.
Numerous methods of achieving this are known in the art, for example, the surfaces of many types of plastic articles such as photographic film, automobile body parts, laminated sheets, packaging films, floor covering materials, plastic bottles and the like, have been subjected to different types of hydrophilizing treatment, such as glow discharge, surface plasma treatment, electric corona discharge, direct or alternating current discharge, microwave discharge, and the like, in order to enhance the ability of the articles to accept adhesives, coatings, paint, printing ink, and the like. A representative list of U.S. patents dealing with this subject includes U.S. Pat. Nos. 3,428,801; 3,888,753; 3,944,709: 4,275,301; 4,467,200; 4,719,533; 4,724,508; and 4,854,999.
Previously, the foregoing technology has not been used for the treatment of casting moulds. The purpose of the technology is to bond materials firmly to the hydrophobic surface and thus prevent release of the materials therefrom, and, since one of the essential characteristics of a casting mould is that it be capable of releasing the moulded article upon completion of the process, the use of such technology has been contradictory.
Further, various chemical reagents, such as solvents, release agents, and reactant vapours, have been used to treat casting mould surfaces for various purposes (e.g. U.S. Pat. No. 4,150,073). However, these systems have not been suggested for modifying an hydrophobic surface of a casting mould to enhance the acceptability of a hydrophilic pigment carrier.
It is an object of the present invention to provide an improved method for producing contact lenses having a colour pattern simulating the iris of the human eye.
It is another object of the invention to provide a method for modifying the surface of a hydrophobic lens casting mould to enhance the adhesion of a hydrophilic monomer colouring dispersion without interfering with the release properties of said mould.
It is a further object of the invention to provide a method for applying a highly effective coloured printed pattern, such as an iris pattern, to an optical lens, using a single monomer or monomer combination as both pigment carrier and lens forming material.
It is a still further object to provide a method for treatment of a hydrophobic casting mould to enhance its ability to hold an optical lens while an optical surface is being generated thereon, without interfering with subsequent release of the lens from the mould.
It is yet another object to treat the surfaces of a two-part optical lens casting mould to promote selective retention of the lens on a designated part of said mould.